The catabolism of some physiologically active polypeptides by homogenate of dog hypothalamus

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Abstract
Incubation of bradykinin, oxytocin, substance P and vasopressin with homogenate of dog hypothalamus at pH 73 and 37[degree] caused a reduction in the biological activity of the polypeptides. The inactivation of the polypeptides is due to enzymes; bradykinin, oxytocin and vasopressin are destroyed most rapidly at pH 7-8, and substance P at pH 6. The general properties of the enzyme destroying vasopressin, taken in conjunction with the effect of some enzyme inhibitors, suggest that it is different from enzymes previously found in brain. Results obtained with mixed substrates suggest that oxytocin and vasopressin are substrates for the same enzyme; substance P appears to be inactivated by a different enzyme.